1. Field of Invention
The present invention relates to a magnetic random access memory and more particularly to a magnetic random access memory having a word line driver and decoder that controls current during read and write operations.
2. Description of Related Art
Typical Magnetic Random Access Memory, MRAM, structures have a nonmagnetic layer sandwiched between two ferromagnetic films. The two ferromagnetic films are also known as magnetic thin films. The MRAM employs the magneto resistive properties of this structure to store data. In each storage element, an MRAM employs two lines, commonly termed a word line and a sense string, in order to detect the magnetization direction of these magnetic thin films. Each string comprises a magnetic thin film that serves as a memory element, and the word line generally addresses multiple sense strings. Magnetic thin films that have a parallel moment have a low resistance and are typically assigned the ‘1’ state. Magnetic thin films having an anti-parallel moment have a high resistance and are typically assigned the ‘0’ state, but may also be assigned to the ‘1’ state.
During a read operation, a word current passes through the word line causing the magnetic layers in the sense string to rotate, thereby changing the resistance in the sense string. A sense current passes through the sense string. A sense line receives the signal from the sense string. A differential amplifier compares the signal from the sense line to a reference line to determine whether a one resistance or a zero resistance is stored in the MRAM. A differential amplifier notes the change in voltage across the sense line to determine resistive state of a storage element.
To implement reliable read and write operations requires the precise generation and control of current on the word line. Turn on transients have the potential to change the state of memory elements in a spurious manner thereby corrupting data integrity.
Thus, there is a need for methods and apparatus for generating a stable and reliable current on the word line.
There is a further need for methods and apparatus for controlling current on the word line.